1. Field of the Invention
The present invention relates to a liquid crystal display device. The invention more particularly relates to a liquid crystal display device including an alignment film provided with alignment controllability by irradiation of light.
2. Description of the Related Art
Liquid crystal display devices include a TFT substrate having pixel electrodes, thin film transistors (TFTs), etc. formed in a matrix; a counter substrate opposing the TFT substrate and having black matrices and an overcoat film, etc.; and liquid crystals put between the TFT substrate and the counter substrate. Images are formed by controlling the light transmittance of the liquid crystal molecules of each pixel.
Since liquid crystal display devices are flat and light in weight, they are applied in various fields, for example, from large-sized display devices such as television sets to mobile phones and DSCs (Digital Still Cameras). For liquid crystal display devices, the view angle characteristic issues a problem. The view angle characteristic is a phenomenon such that the luminance or chromaticity changes from that of when the screen is viewed from the front when the screen is viewed from an oblique direction. The IPS (In Plane Switching) system which operates liquid crystal molecules by a horizontal electric field has a good view angle characteristic.
As a method of alignment treatment, that is, a method for giving alignment controllability to an alignment film used for liquid crystal display devices, rubbing treatment has been used in the conventional art. Rubbing treatment is performed by rubbing an alignment film with a cloth. On the other hand, there is a method called an optical alignment method which can provide alignment controllability to an alignment film in a contactless manner. Since the performance of the IPS system is better as the pre-tilt angle is smaller, the optical alignment method which in principle does not generate a pre-tilt angle is advantageous.
The TFT substrate and the counter substrate are bonded at their periphery with a seal material; as the seal material, UV-curable resin is often used. When the display region in which the alignment film is formed is irradiated with UV-light to cure the seal material, the UV-light deteriorates the alignment film. Conventionally, a light shielding mask has been used so that the display region is not irradiated with UV-light upon the UV-irradiation against the seal material.
However, even when such a mask is used, the UV-light comes around to deteriorate the alignment film at the periphery of the display region. JP-A-H10-221700 discloses a configuration in which the counter substrate is provided with a band pass filter surrounding the outer side of the display region so that it cuts off the UV-light, thereby protecting the alignment film and liquid crystals in the display region from the UV-light by the combination of the light shielding mask and the band pass filter.